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Even a plate of farm-fresh greens or a chunk of prime meat sometimes needs improvement. From a culinary standpoint, it’s the flavor of the dressing or sauce that makes the meal, but from a technical perspective, the viscosity of these products can be equally important.

Salad dressings have enjoyed a long history in the global diet. According to the Association for Dressings and Sauces (ADS), Atlanta, oil and vinegar on greens was popular with the Babylonians more than 2,000 years ago. The Egyptians enjoyed their greens with oil, vinegar and Oriental spices, and the Romans dressed their salads with salt. In fact, “salad” is derived from the Latin words herba salta, meaning salted herbs. Mayonnaise is reportedly a byproduct of the French celebration of the capture of Mahon, a Spanish city on the Isle of Minorca. According to an ADS 1997 Gallup survey of 1,004 participants, 93% of adults either always or usually used a dressing on their salads. Ranch-style dressings are No. 1 in popularity, followed closely by Italian, creamy Italian and Thousand Island.

Many foods, both savory and sweet, are enhanced and complemented by sauces, a thickened, flavored liquid that can be used either before or after cooking. French chef Antonin Carême, founder of La Grande Cuisine Francaise, the classic French style of cooking, is often credited with the development of the modern sauce, classifying them as one of five “mother sauces.” Yet for thousands of years, sauces have been used throughout the world, from Mexican adobo and ranchero sauces to Chinese hoisin and plum sauces.

Defining dressings and saucesWhatever the pedigree, salad dressings and sauces cover a wide range of products that have a wide range of ingredients. These ingredients and the methods used to combine them will always contribute to the finished product’s viscosity.

Salad dressings are oil-in-water emulsions — oil is the discontinuous phase and water is the continuous phase. The emulsion gives the dressing body and the quality of the dressing depends on this emulsion’s stability. Typically, the smaller the oil droplet, the more stable the emulsion. Often, especially for long-term shelf life, emulsification agents that contain both polar and nonpolar groups, such as phospholipids, are required to keep the droplets from coalescing. The emulsifiers orient themselves between the two phases (the polar groups are attracted to the water phase and the nonpolar regions to the fat phases) and create a kind of barrier around each droplet.

Salad dressing has two general classifications based on viscosity: pourable (a thinner, flowable product) and spoonable (a thicker, more plastic product). However, there are standards of identity for only three types of salad dressings in the Code of Federal Regulations (CFR) — French dressing (21 CFR 169.115), mayonnaise (21 CFR 169.140) and salad dressing (21 CFR 169.150).

Mayonnaise is spoonable and has specific ingredients and levels defined in its standard of identity. It is defined as the “emulsified semisolid food prepared from vegetable oil(s),” with vinegar(s) having an acidity calculated as acetic acid of not less than 2.5% (lemon or lime juice also may be used, with acidity as citric acid). Vegetable-oil content must be at least 65% by weight, and mayonnaise must contain an egg-yolk-containing ingredient (liquid yolks, frozen yolks or whole eggs — liquid, frozen or dried). This egg yolk contains phospholipids that help form and maintain the emulsion. No starches or gums may be used to assist in thickening — spices and other optional ingredients are specifically noted in the standard.

On the other hand, salad dressing is defined by the CFR as: “The emulsified semisolid food prepared from vegetable oil(s),” …acidifying ingredients as specified, egg yolk solids as specified, and a starch paste as specified. Again, vinegar(s), lemon juice or lime juice may be used, but no minimum acetic acid or citric acid levels are noted. Vegetable oil must not be less than 30% by weight, and there is a minimum amount of egg-yolk solids specified (4%). The starch must be a food starch or modified food starch; tapioca flour, wheat flour, rye flour, or a combination may also serve as thickeners. Again, the standard lists a number of optional ingredients: salt, nutritive carbohydrate sweeteners, spices (except saffron or turmeric) or natural flavorings, monosodium glutamate, dioctyl sodium sulfosuccinate, citric and/or malic acid, sequestrants, and crystallization inhibitors.

Of the many other products sold in the salad-dressing category, French dressing, which may contain no less than 35% vegetable oil, is the only other dressing that has a standard of identity, and stabilizers and thickeners are not excluded from that. The CFR defines French dressing as “the separable liquid food or the emulsified viscous fluid food prepared from vegetable oil(s) and one or both of the acidifying ingredients (vinegar, lemon juice and/or lime juice)…” One or more of the ingredients specified as optional ingredients — similar to the list for salad dressing, with the addition of tomato ingredients, eggs and coloring agents — also may be used.

The term “sauce” is much more undefined than dressing, and so any ingredient discussion regarding sauces must take into account the type of sauce, manner of processing, expected use and required shelf life. The dictionary defines sauce as “a flavorful liquid dressing or relish served as an accompaniment to food.” This says nothing about other ingredients, viscosity, percent of fat or optional ingredients — there is no standard of identity. In classic culinary terms, you might consider the five “mother sauces” (espagnole, or brown sauce; béchamel, or cream sauce; velouté, or fricassee; hollandaise; and tomato sauce). These might give some general ingredient guidance, but do not by any stretch of the imagination cover the entire gamut of products called sauces, especially for the processed-foods industry.

Many sauces are emulsions of fat and water, but that is not a requirement. Where salad dressings are usually acidified, preserved through the use of chemical preservatives, or refrigerated, sauces may be retorted, frozen or refrigerated, then heated prior to serving. They may be dairy-based, savory meat- or vegetable-based, tomato-based, high acid, low acid, liquid, thick or gelled. Gravies often contain fat and, very often, flour as well. Many factors can impact the product’s quality and shelf-stability, and a wide range of stabilizers can be considered based on the usage and end result desired.

Building viscositySo what supplies the thickening and stabilization to mayonnaise and salad dressings, as well as gravies and sauces? The more solids in the finished product, the thicker it will be. First of all, define the total solids. This would include the vegetable (or animal) oil or fat selected, egg-yolk solids, sugar (if added), and all of the optional ingredients added, including vegetable pieces, spices, starches and gums. But obviously, each will have a different effect based on the physiochemical effects they produce — a 5% sugar solution will have a vastly different effect on viscosity than a 5% starch solution that has undergone heating to its gelatinization temperature.

The emulsion also contributes to viscosity, so processing will impact viscosity as well as stability. Most commercial mayonnaises contain 77% to 82% vegetable oil to reach the best viscosity, so processing is the key to keeping the oil in the discontinuous phase. If a stable emulsion is achieved at this fat level, mayonnaise becomes a “Bingham plastic” — it acts like a solid until its yield value (the amount of shear stress needed to cause a solution to flow) is exceeded. At that point, its flow rate is directly proportional to the shear stress applied.

In salad dressings and sauces, thickening and stabilization are also a function of the starch paste, gums and other optional ingredients, such as emulsifiers and dairy powders or other proteins. The starches, gums and proteins all increase viscosity by gel formation and/or by swelling of the granules when moisture is absorbed. The types of gels formed vary with the stabilizer used and other ingredients in a particular formulation that might affect its performance, ranging from weak, highly flowable gels to stiff, even brittle, gels. Depending on the hydrocolloid system used, these can display a wide range of rheological characteristics, including shear-thinning and thermoreversibility.

Emulsifiers, on the other hand, promote and stabilize the structure formed by the colloidal structure of two immiscible liquids, oil and water, in emulsion form. Many are fat derivatives, such as mono- and diglycerides, but they may come from a wide variety of ingredients. Proteins also can act as emulsifiers by forming a film around dispersed oil droplets. Because gum arabic contains both hydrophilic and lipophilic areas on its molecule, it too exhibits emulsification properties.

In addition to source, emulsifiers can be classified based on their hydrophilic-lipophilic balance (HLB), a measure of the ingredients’ attraction for water and oil. While there are no hard-and-fast rules, an emulsifier with a low HLB (more lipophilic, or nonpolar) will tend to work better in a water-in-oil emulsion, while a high HLB (more hydrophilic, or polar) favors oil-in-water emulsions. But, because most dressings and sauces will consist of complex ingredient systems vs. a simple water-and-oil mixture, many other factors come into play in determining the correct emulsifier.

Heavy on the starchStarch is one of the most widely used stabilizers in dressings and sauces. “Spoonable dressings are mainly cook-up systems,” notes Celeste Sullivan, senior applications specialist, Grain Processing Corporation, Muscatine, IA. “The starch ‘paste’ would be cooked in a jacketed kettle, through a plate heat exchanger or through a steam-injection system (more continuous), then cooled. If modified starch is used, it is often a blend of waxy and dent cornstarch. The waxy portion provides the smooth, creamier texture and the dent portion provides the ‘set,’ or more cutable texture. The ratio of the blend will be varied and may sometimes include an unmodified dent cornstarch that will retrograde, setting to a firmer gel structure.”

A quick starch primer is in order here. Starch is composed of two polymer types — the higher-molecular-weight, branched-chain amylopectin and the straight-chain, more retrogradable amylose. “Waxy” corn is a hybrid, containing starch composed almost entirely of amylopectin. Dent, sometimes called “common” corn, is composed of about 28% amylose and 72% amylopectin. Because of the amylose content, the dent corn more readily retrogrades, forming a gel. The straight-chain amylose can more readily align or collapse upon itself into tight bundles, forming a stiff structure and squeezing water out, resulting in syneresis. The result, depending on solids, is precipitation or gelation. The branched-chain amylopectin is less likely to become closely aligned, so moisture is retained, forming a creamier-textured product with less gel.

The ingredients chosen to thicken a salad dressing also must be matched to the chosen process. The general procedure is to combine the starch, water, vinegar, sweeteners and spices, then cook the starch to gelatinize it, and then chill the mixture. Eggs, oil and seasonings are batched and then chilled. Both components meet in a pre-emulsion mixer, which blends them through a colloid mill to create a uniform, stable emulsion that is then pumped to a filler.

For the starch slurry portion of the process, the industry uses many types of equipment — batch cooking (open kettle), plate-heat exchanger, jet cooker, swept-surface heat exchanger or cold process. Cold process involves ingredients that will hydrate in cold water, so proper gum selection and use of pregelatinized starches is important. Starch selection will depend on the type of equipment and optimum viscosities throughout the process. A starch or starch combination must be selected to fit the process — by the proper use of crosslinking to improve acid, heat and shear stability, and the use of modification and/or amylose-to-amylopectin ratios to control creaminess, firmness and product flow.

Stabilize in an instantStarch can be used in applications that do not incorporate a heating step during manufacturing or for “just-add-water” dry mixes. Instant starches are made either by precooking them on a hot roll, through an extruder, or by preswelling the granules and drying them intact. A.E. Staley, Decatur, IL, developed a number of these “granular” cold-water-swelling (CWS) starches several years ago. These starches generally form a smoother dressing with more sheen than traditional drum-dried pregelatinized starches. Drum-dried starches give the product a grainier appearance that may be appropriate for some sauces and dressings. A range of CWS starches has been developed for cold-water gelling or thickening purposes, and has better dispersion and flow characteristics for use in dry mix dressings or sauces.

While most food product designers automatically think of corn-based starches, other CWS starches are available. Sally Brain, director of marketing, food and new business, Avebe America Inc., Princeton, NJ, notes that her company has introduced a range of potato- and tapioca-based CWS starches based on patented technology. “Because of the high viscosity and clarity of potato starch, CWS potato starches can be used at a lower level or as partial xanthan-gum replacements in Italian-type dressings,” she says. “They also exhibit thin/thick shear properties important to the processor.” Potato starch and tapioca starch are noted for clean flavor, and have better label appeal in some products.

Cold processing is growing in the dressing industry because of savings in time, labor, energy and equipment. Plus, “a pregelatinized starch can reduce the level of gum usage by as much as 60%,” explains Sullivan.

Viscosity, by gumIf pourability is to be best controlled, most dressings will use a xanthan gum or a combination of xanthan and propylene glycol alginate (PGA), says Karen Freese, marketing manager, xanthan gum, ADM Food Additives, Decatur, IL. “Xanthan gum provides an excellent stable emulsion, and PGA will interact with xanthan for smoother flowing out of the bottle,” she notes.

Xanthan is a unique microbially produced polysaccharide with excellent stability to heat, pH, high salt levels and enzymatic attack. When a xanthan-gum solution is poured, mixed or pumped, it shows a dramatic fall in viscosity, then returns to its initial viscosity when the shear stress is removed. This is ideal for products that must flow from a bottle, yet cling to the surface of the food on which it’s being poured. PGA was widely used a number of years ago, but the versatility and wide use range of xanthan gum has allowed it to take over in many applications.

“Xanthan gum has become the ‘sugar’ of the gum industry” notes Alan Freed, president, Gum Technology, Tucson, AZ. “Most manufacturers do not want to stock multiple ingredients, so xanthan gum, PGA and guar gum (the ‘salt’ of the industry) are predominately used. This does not necessarily mean that these are the best in each application. Locust bean gum will make a dressing with a nicer texture with no syneresis in some cooked applications, and often is more cost effective. Carrageenans work well in many applications, and we have had some success with konjac flour in sauces and gravies — it produces a high viscosity, so use levels can be very low.”

PGA, a derivative of alginic acid, displays good acid stability and low reactivity with calcium. The degree of esterification is controlled to provide a range of PGA with low to high viscosity. PGA also provides thickness/ creaminess, mouth-coating and a slow dissolution rate in the mouth. “PGA provides a high degree of emulsification,” says Freed. “In dressings which require phase separation, such as a natural-appearance Italian dressing, a small amount of PGA will temporarily hold the combined phases together after shaking until the dressing is poured, then allow the phases to separate when the bottle is placed back on the table.”

As indicated by Freed, many labels show combinations of xanthan gum with guar gum. Guar gum is a seed gum commonly used to build viscosity at lower cost, and many manufacturers have become very comfortable with it. It is synergistic with xanthan gum, but by itself has a slimy mouthfeel and less desirable flavor. Guar is cold-water soluble and provides a measure of freeze/thaw stability to products.

Guar gum and carboxy methylcellulose (CMC) have a flatter viscosity vs. shear rate profile than xanthan — they provide viscosity without the advantage of pseudoplastic flow. A viscosity profile also shows that as shear is removed, a 0.25% xanthan gum solution builds in viscosity to a level much higher than guar or CMC.

The structure of xanthan gum vs. other natural gums allows it to rapidly dissociate and align in the direction of flow, then to re-associate when shear is stopped. This causes the viscosity to rapidly decrease as the molecules align during pouring, then increase back to the original viscosity when the product is at rest, allowing particles to remain in suspension. Other gums dissociate more slowly, then do not re-associate as easily.

Gums also are available that, through patented technology, improve upon xanthan’s ability to disperse and hold particles in solution at lower viscosity, says Freed. Xanthan exhibits excellent solubility and stability under acidic conditions and in the presence of salts, making it highly suitable for salad-dressing applications. Methylcellulose is another product that works as a thickener, emulsifier or suspension agent, and it helps to control syneresis on storage or during freeze/thaw cycles. Methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC) cold-water-soluble cellulosic gums exhibit a reversible thermal-gelation effect.

Methylcellulose increases the viscosity during heating, and can compensate for the thinning of other viscosifiers. An example of its use is its synergy with starch to control the viscosity of potpie sauces during reheating to prevent boil-out. In tests performed by the Dow Chemical Company, Midland, MI, sauces containing xanthan gum or CMC with starch lost viscosity as they were heated in an oven, with subsequent boil-out. A sauce with 3.30% starch and 0.15% methylcellulose developed a lower initial viscosity, but thickened during static heating in an oven, resulting in no boil-out.

Other hydrocolloid systems can be incorporated to provide specific characteristics. CMC gum is a stable thickener that exhibits synergies with guar. Cellulose gels are coprocessed mixtures of microcrystalline cellulose and either xanthan gum or guar gum. Alginates and carrageenans are derived from seaweed. When calcium ions are present, alginates form thermally irreversible gels that stand up to heat and work in systems with very low solids. Carrageenans can form a wide range of structures, from kappa carrageenan’s, strong, rigid gels, to lambda carrageenan’s pseudoplastic thickening in combination with protein.

The plot thickensThickening and stability also may be adjusted or modified through use of an emulsifier. “Lecithin can be used in creamy salad dressings and in sauces, and is particularly effective in low-fat or fat-free formulations,” states Lance Colbert, manager of lecithin technical services, ADM Lecithin and Monoglycerides. Lecithin has natural label appeal, and serves many functions — emulsification, crystal modification, instantizing, release agent, viscosity modification and lubricity.

Distilled monoglycerides generally are not used in salad dressings (particularly cold–process versions) because of the temperature required to activate them, says Dawn Sikorski, research chemist, ADM Lecithin and Monoglycerides. They can be found in buttermilk dressings where the buttermilk is preprocessed. Monoglycerides, like lecithin, typically are used in fat-free salad dressings to impart a creamier, more fat-like mouthfeel. Mono- and diglycerides also can have an impact in canned products, for reduction of “fat-capping,” where fat separates and rises to the surface. Alternatively, they can delay starch gelatinization to make heat transfer more efficient. For sauces, Sikorski recommends 2.0% to 4.0% of the total fat (0.2% to 0.4% monoglyceride for a 10.0% fat product).

Proteins can provide viscosity and some emulsification to dressings and sauces. “Functional soy protein concentrates can be an effective emulsifier in savory sauces,” explains Russ Egbert, director of protein applications research, ADM Protein Specialties. “Soy protein isolate can replace egg solids 1:1 in a salad dressing or hollandaise sauce, resulting in a low-process viscosity prior to the colloid mill.” Another application, according to Tom Gottemoller, manager of food process research, ADM Protein Specialties, is buttermilk-based ranch dressings. “A 4.5% solution of soy protein isolate has a low process viscosity, but thickens with acid and shear, giving the product the look and feel of buttermilk.”

Many other ingredients can work in salad dressings and sauces, and choice is dictated by the end result or label appeal desired. Maltodextrins may be present as carriers or dispersing aides; they are excellent bulking agents and opacifiers with low flavor impact, and may be seen on labels for this purpose. Inulin has been used in commercial applications primarily for its appeal as a probiotic, but it can be considered as a bulking agent, soluble fiber, bifidus-stimulating agent or as a dispersing agent. This carbohydrate polymer also adds rheological and textural properties to foods, including sauces, gravies and dressings, especially in no- and low-fat applications. Inulin has synergistic effects with other gum-based stabilizers, thickeners and gelling agents.

Best useIf the viscosity does not develop properly, do not automatically blame the ingredient. Contrary to your experience assembling toys under the Christmas tree, you should read the instructions first when using instant starches and gums. “The gums and instant starches (pregelatinized) are difficult to disperse, often causing lumps or fish-eyes,” says Sullivan. “These starches are typically waxy- or dent-based, and require a diluent (oil, corn syrup, sugar, maltodextrin, spice, salt) or high-shear mixing to incorporate them.”

Shelf-life stability studies are important when selecting starches and gums. Using an unmodified starch to stiffen gel structure may seem attractive, but could cause the dressing or sauce to continue to retrograde, resulting in syneresis or pulling away from the sides of the container. Also, gums and starches could continue to hydrate on the shelf, increasing the viscosity of the product. According to Sullivan, “The products going to the retail market are expected to have a one-year shelf life; the foodservice market expects only a three-month shelf life.”

When considering ingredients, the developer must consider all stages of product assembly and use. Are viscosifiers needed to suspend particulates during pumping? What pieces of equipment are used to heat starches and gums? Is an emulsion required?

For the ingredients themselves, the developer must consider dispersion time, hydration rates, gelation, gelatinization temperature and range, melting points, heat, shear, shelf and pH stability, ingredient interactions, retrogradation, preservation and contamination. The ingredients must be matched to the process system, which is never a given in the dressing and sauce industries. Steam-jacketed kettles and Hobart-type mixers are low shear, but pumps, pipes, homogenizers and colloid mills can all shear-stress the product. Prior to the colloid mill, choice of mixers and heat exchangers also can impact the product.

Combining the requirements of process and finished product and coming up with the right ingredient isn’t always easy. However, the wide range of available choices in stabilizers for dressings and sauces gives product designers a host of options that address nearly every need.

Ronald C. Deis, Ph.D., is the director, product and process development at SPI Polyols Inc., New Castle, DE. Deis has 20 years of experience in the food industry, both in food ingredients (starches, polyols, high potency sweeteners, bulking agents) and in consumer product companies (cookies, crackers, soups, sauces). He has been a short-course speaker (polyols, fat replacers) and a freelance writer on a number of food-science-related subjects in food journals, and has contributed chapters on sweeteners and fat replacers for several books.